Spherical microparticles containing linear polysaccharides

ABSTRACT

Microparticles with a uniform spherical shape and a very narrow size distribution are described. They consist wholly or partly of a linear water-insoluble polysaccharide, preferably of 1,4-α-D-polyglucan, and may contain other, in particular biodegradable, polymers and/or active substances. They are suitable inter alia for the controlled delivery of active substances. They are prepared by dissolving 1,4-α-D-polyglucan or the polysaccharide in a solvent, introducing the solution into a precipitant, cooling the mixture and removing the particles formed.

The invention relates to spherical microparticles which contain linearpolysaccharides, to processes for their preparation and to their use, inparticular for controlled delivery of active substances.

Processes for preparing particles, especially microparticles frompolymers such as, for example, polysaccharides, for a wide variety ofapplications are quite complicated processes which require accuratecompliance with various parameters. In particular, many processes alsoresult in only low yields and in very wide particle distributions.Mention should be made in this connection in particular of spray drying,interfacial condensation and emulsion processes (for example WOprocesses=water-in-oil emulsions, WOW=water-in-oil-in-water emulsions,coacervation, phase separation, dispersion). Emulsion processes inparticular, but also spray dryings from two-phase systems, require avery accurate procedure and, in most cases, the use of auxiliaries(emulsifiers). Stable emulsions can often be prepared only at greatexpense and with precise control of a large number of parameters(temperature, stirring speed etc.), and comprehensive removal of theparticles involves problems. The yield of particles is often very lowand, in particular, the proportion of active substances entrapped isinadequate. This is as an aspect which may prevent application of atechnology in the case of costly pharmaceutical active substances.

Spherical microparticles which, besides tartaric acid-containingpolycondensates, which may also contain ethyl starch or otherpolysaccharides are obtained, according to U.S. Pat. No. 5,391,696, onthe one hand by the spray-drying process, but with this the particlesize and, in particular, the size distribution can be controlled onlywith great difficulty. Another possibility described in this patent isdissolving the polymer in a solvent or mixture of solvents and dropwiseaddition of the solution to a cold liquefied gas, for example liquidnitrogen, with formation of spherical particles. The small beads canthen be introduced into water, which simultaneously precipitates thepolymer and extracts the solvent. This process is time-consuming, costlyand uneconomic. The uniformity of the particle dimensions is alsounsatisfactory.

EP-B1-0 251 476 describes the preparation of microparticles frompolylactides in which a macromolecular polypeptide is dispersed.Intensive control of a wide variety of parameters is necessary in thiscase too. Uniform spherical particles are not obtained.

Microparticles which contain active substances and gases are describedin WO 95/07 072. Preparation takes place by elaborate emulsionprocesses, and the size distribution of the particles is veryinhomogeneous.

Yu Jiugao and Liu Jie report in starch/stärke 46(7)252-5(1994) on theeffects of the suspension crosslinking reaction conditions on the sizeof starch microbeads. The crosslinking takes place in three stages; themedium is a water-in-oil suspension, and a peanut oil/toluene mixture isused as oil phase. Pregelatinized starch is added as aqueous solutionwhich also contains sodium hydroxide and ethylenediaminetetraaceticacid. The presence of a surface-active agent or stabilizer is alsonecessary.

The disadvantage of the process described therein is that the resultdepends on a large number of factors, namely on the density, theviscosity and the concentration ratios both of the aqueous and of theoil phase, on the stabilizer and on the stirring speed, and, inaddition, the presence of the stabilizer is disadvantageous. It ismoreover difficult to control the large number of parameters given, sothat the reproducibility is unsatisfactory.

Particles which are loaded with macromolecular active substances and arecomposed of water-insoluble polymers such as polylactic acid orethylcellulose are obtained, according to the disclosure of EP-B1-0 204476, by suspending the particulate active substance in an acetonesolution of the polymer, and evaporating off the solvent at roomtemperature. The particles resulting in this case still do not show therequired pharmacological effects, so that further processing toso-called pellets is necessary.

Although microparticles with a spherical shape and processes forpreparing them are already known, there is still a need for suchmicroparticles with improved properties, and for more advantageous, inparticular economic and easily reproducible, preparation processes. Itis therefore an object of the invention to provide microparticles whichhave a substantially regular spherical shape and which in addition showa size distribution which is as narrow as possible, i.e. a greatuniformity, and which can be used for many purposes. Another object ofthe invention is to provide a process for preparing such microparticleswhich is simple and economic to carry out and which providesmicroparticles with regular structures and great uniformity, which havegood mechanical properties, which are biodegradable, which can beprovided with a wide variety of active substances, and which areparticularly suitable for controlled delivery of active substances.

This object is achieved by spherical microparticles having an averagediameter of from 1 nm to 100 μm, consisting wholly or partly of at leastone water-insoluble, linear polysaccharide.

Spherical microparticles mean microparticles which have approximately aspherical shape. If a sphere is described by axes of equal length whichare directed into space from a common origin and define the radius ofthe sphere in all directions in space, the length of the axes maydeviate from the ideal spherical shape by from 1% to 40% for thespherical microparticles. Spherical microparticles with deviations of upto 25% are preferably obtained, particularly preferably up to 15%. Thesurface of the spherical microparticles can be compared macroscopicallyto that of a raspberry, it being intended that the depth of the“recesses” or “indentations” is not more than 20% of the averagediameter of the spherical microparticles.

“Linear, water-insoluble polysaccharides” for the purpose of the presentinvention are polysaccharides which are composed of monosaccharides,disaccharides or other monomeric building blocks in such a way that themonosaccharides, disaccharides or other monomeric building blocks arealways linked together in the same way. Each basic unit or buildingblock defined in this way has exactly two linkages, in each case one toanother monomer. Exceptions to this are the two basic units which formthe start and end of the polysaccharide. These basic units have only onelinkage to another monomer. When there are three linkages (covalentbonds), a branch is said to be present. Linear, water-insolublepolysaccharides for the purpose of the invention have no branches or, atthe most, to only a minor extent, so that with very small proportions ofbranches they are not accessible to conventional analytical methods.

The term “water-insoluble polysaccharides” means for the presentinvention compounds which fall into the categories of ‘sparinglysoluble’, ‘slightly soluble’, ‘very slightly soluble’and ‘practicallyinsoluble’ compounds as defined in the German Pharmacopeia(DAB=Deutsches Arzneibuch, Wissenschaftliche Verlagsgesellschaft mbH,Stuttgart, GoviVerlag GmbH, Frankfurt, 9^(th) edition, 1987),corresponding to classes 4 to 7.

Preferred within the scope of the invention are linear, water-insolublepolysaccharides which have been prepared in a biotechnological, inparticular in a biocatalytic, also biotransformation, or a fermentationprocess.

Linear polysaccharides prepared by biocatalysis (also:biotransformation) within the scope of this invention means that thelinear polysaccharide is prepared by catalytic reaction of monomericbasic building blocks such as oligomeric saccharides, for example ofmono- and/or disaccharides, by using a so-called biocatalyst, normallyan enzyme, under suitable conditions.

Linear polysaccharides from fermentations are, in the terminology of theinvention, linear polysaccharides which are obtained by fermentationprocesses using naturally occurring organisms such as fungi, algae orbacteria or using non-naturally occurring organisms but with theassistance of natural organisms which have been modified by geneticengineering methods as generally defined, such as fungi, algae orbacteria, or can be obtained with the involvement and assistance offermentation processes.

Linear polymers according to the present invention may, besides thepreferred 1,4-α-D-polyglucan, also be other polyglucans or other linearpolysaccharides such as, for example, pullulans, pectins, mannans orpolyfructans.

It is additionally possible to obtain linear polymers for preparing themicroparticles described in the present invention also from reaction ofother nonlinear polysaccharides by treating nonlinear polysaccharideswhich contain branches with an enzyme in such a way that cleavage of thebranches occurs, so that linear polysaccharides are present afterremoval thereof. These enzymes may be, for example, amylases,isoamylases, gluconohydrolases or pullulanases.

In a particularly advantageous embodiment of the invention, thespherical microparticles consist wholly or partly of 1,4-α-D-polyglucan.The 1,4-α-D-polyglucan is preferably prepared by a biocatalytic(biotransformation) process using polysaccharide synthases or starchsynthases or glycosyltransferases or α-1,4-glucan transferases orglycogen synthases or amylosucrases or phosphorylases.

The molecular weights M_(w) of the linear polysaccharides used accordingto the invention may vary within a wide range from 10³ g/mol to 10⁷g/mol. The molecular weights M_(w) preferably used for the linearpolysaccharide which is preferably used, 1,4-α-D-polyglucan, are in therange from 10⁴ g/mol to 10⁵ g/mol, in particular 2×10⁴ g/mol to 5×10⁴g/mol.

It has now been found, surprisingly, that very uniform microparticlescan be prepared in large quantities by a very simple process fromwater-insoluble linear polysaccharides, and cannot be obtained in thisway from commercially obtainable polysaccarides such as, for example,amylose or starch.

The invention therefore also relates to a process for preparingspherical microparticles which consist wholly or partly ofwater-insoluble, linear polysaccharides, in particular1,4-α-D-polyglucan, by dissolving the water-insoluble, linearpolysaccharide or the 1,4-α-D-polyglucan in a solvent, introducing thesolvent into a precipitant, cooling the mixture resulting therefrom, andremoving the microparticles formed. Claims 20 to 23 specify particularlyadvantageous embodiments of the process according to the invention.

In another advantageous embodiment, the linear, water-insolublepolysaccharides have been prepared by enzymatic treatment of branched orhighly branched polysaccharides.

Dimethyl sulfoxide is the preferred solvent for dissolving the linearpolysaccharides; other possible solvents are, inter alia: formamide,acetamide, N,N-dimethylformamide, N,N-dimethylacetamide,N-methylmorpholine N-oxide in the presence of water, and otherN-substituted morpholine N-oxides, aqueous solution with high or low pH.

Water is the preferred precipatant; the process can be influenced byusing other solvents which are able to replace water wholly or partly,for example dichloromethane, it being possible to control inter alia theduration of the precipitation process and the texture of the surface ofthe particles. Mixtures of water with alcohols, for example methanol,ethanol, isopropanol, are also suitable for influencing the processparameters and the properties of the particles.

The temperature during the precipitation process is generally preferablyin the range from 0° C. to −10° C., but higher or lower temperatures canalso be taken.

The precipitation process can be carried out relatively slowly at lowtemperature overnight or be influenced by varying the precipitant andthe temperature.

It is possible by also using suitable additives to exert an influence onthe properties of the particles such as the size, the texture of thesurface etc., and on the process controls. Examples of suitableadditives are surface-active substances such as sodium dodecyl sulfate,or N-methylgluconamide, sugars, for example fructose, sucrose, glucose.

The surface-active substances may be anionic, cationic or nonionic innature.

General examples of surface-active substances are: polysorbates (forexample Tween®), alkyl polyglycoi ethers, ethylene oxide/propylene oxideblock copolymers (for example Pluronic®), alkyl polyglycol ethersulfates, alkyl sulfates (for example the sodium dodecyl sulfate whichhas already been mentioned), fatty acid glycol esters. The additives arepreferably added to the precipitant.

The concentration of the linear polysaccharide in the solution may bevaried within wide limits but is preferably 0.1 g of polysaccharide per1 ml of solvent.

Other ranges such as 0.05 g/ml to 0.2 g/ml or 0.02 g/ml to 0.5 g/ml arepossible.

The particles according to the invention may consist of at least onelinear polysaccharide and may contain at least one active substance. Thesurface can be smooth or rough.

The microparticles may be composed of a single linear polysaccharidesubstance, in particular 1,4-α-D-polyglucan. However, it is alsopossible to admix another linear water-insoluble polysaccharide. Otherpolymers, especially other biocompatible polymers, can also be used too.The quantity of the other polymer(s) which can be admixed withoutaltering disadvantageously the spherical shape and other good propertiesof the microparticles always depends on the added polymer. It may be upto 10% or more, and less in certain cases. The maximum quantity which isstill acceptable can easily be determined by a few mixing tests.

The particles may have average diameters (number average) such as 1 nmto 100 μm, preferably 100 nm to 10 μm, particularly preferably 1 μm to 3μm.

The particles show a characteristic of the diameters d_(w) to d_(n) of(dispersity) 1.0 to 10.0,

preferably 1.5 to 5.0,

particularly preferably 2.0 to 2.6

d_(n)=number average diameter

d_(w)=weight average diameter

The averages used herein are defined as follows:

d_(n)=Σn_(i)×d_(i)/Σn_(i)=number average

d_(w)=Σn_(i)×d_(i) ²/Σn_(i)×d_(i)=weight average

n_(i)=number of particles with diameter d_(i),

d_(i)=a particular diameter,

i=serial parameter.

The term “weight” does not in this case represent mass but represents aweighted mean. The larger diameters are given greater importance; thepower of 2 gives greater weighting to diameters of larger particles.

The dispersity of the distribution of the diameters of the particles isdefined as: D=d_(w)/d_(n)

The heterogeneity of the distribution of the diameters is defined as:

U=d _(w) /d _(n)−1=D−1

A heterogeneity value closer to “0” means the particles are shaped moreuniformly in respect of their size distribution. The microparticles canbe employed advantageously, particularly also because of their uniformshape and size, in a wide variety of applications, either as such inpure form or by entrapping active substances in the widest sense, thus,for example,

as additives for cosmetics in ointments, dusting powders, creams, pastesetc.,

as vehicles for active substances in pharmaceutical and otherapplications,

as smoothing agents, for example for closing pores or smoothing flashes,

as food additive, for example as bulking component or for improvingrheological properties,

as additive for upgrading, for example, emulsion polymers,

as separation aids, for example in the removal of impurities,

as encapsulating material,

as carrier for magnetic particles,

as filler for biodegradable polymers or industrial polymers forcontroling properties,

as additive for controling properties, for example the porosity, theweight, the color etc.,

as particle standard for calibration or determination of the particlesize of unknown materials.

Individual active substances or combinations of active substances can befound, for example, in the following list:

pharmaceutical active substances, medicines, medicinal substances,peptides, proteins, nucleic acids, vaccines, antibodies, steroids,oligonucleotides, flavorings, perfumes, fertilizers, agrotechnicalactive substances such as pesticides, herbicides, insecticides,fungicides, chemicals with specific properties such as luminousmaterials, emulsifiers, surfactants, pigments, oxidants, reductants,fullerenes, magnetic complexes, for example paramagnetic compounds.

The invention thus also relates to the use of the microparticlesdescribed above for controlled, for example delayed, delivery of activesubstances.

The process comprises a very simple procedure. The parameters forpreparing the particles can be specified within wide ranges, such as theratio of solvent to precipitant, temperature during the precipitationprocess, concentration of the solution, rate of addition of the solutionto the precipitant.

The particles are distinguished by a great uniformity in terms of theirsize and the distribution of their diameters.

The insolubility in water of the initial polymer, for example1,4-α-D-polyglucan, makes it possible to implement particularlyadvantageous applications which are not out on a rapid destruction ofthe microparticles and can therefore also be used particularlyadvantageously in products in which water is present as anothercomponent.

The microparticles are distinguished by the ability to be exposed tohigh mechanical stressability.

In particular, because of their morphology and uniformity, the particleshave a smoothing effect, for example on pores.

The 1,4-α-D-polyglucan which is preferably employed can be prepared invarious ways. A very advantageous method is described in WO 95/131 553.The disclosure in this publication is incorporated herein by reference.

The invention is explained in detail by means of the following examples.

EXAMPLE 1 Preparation of Microparticles of 1,4-α-D-polyglucan

500 mg of 1,4-α-D-polyglucan are dissolved in 2.5 ml of dimethylsulfoxide (DMSO, analytical grade, from Riedel-de-Haen) at about 70° C.The DMSO solution is added dropwise to 100 ml of double-distilled waterwith stirring, and the solution is kept at 5° C. overnight. The finemilky suspension is centrifuged at 3500 revolutions per minute for 15minutes and the supematant is decanted off. The sediment is suspended indouble-distilled water and centrifuged again. The procedure is repeatedtwo more times. The suspension is subsequently freeze-dried. 311 mg ofwhite 1,4-α-D-polyglucan particles are obtained. This corresponds to ayield of 62% of colorless microparticles.

EXAMPLE 2 Attempt to Prepare Microparticles From Amylose Isolated FromPlants

500 mg of amylose (from potatoes, from EGA-Chemie) are dissolved in 2.5ml of dimethyl sulfoxide (DMSO, analytical grade, from Riedel-de-Haen)at about 70° C. The DMSO solution is highly viscous. It is added withstirring to 100 ml of double-distilled water, and the solution is keptat 5° C. overnight. A white flocculant suspension forms. The furtherprocessing takes place as described in Example 1. 210.3 mg of a whitesolid are obtained (42% yield) which comprises non-particulatestructures.

EXAMPLE 3 Attempt to Prepare Microparticles From Amylose Isolated FromPlants

This attempt is carried out in analogy to Example 2. 500 mg of amylosesupplied by Merck (manufacturer's statement: “Amylose for biochemicalpurposes”) are employed. After the period of standing overnight, a whiteflocculant suspension has formed. Further processing takes place asdescribed in Example 1. 60 mg of a white solid are obtained (12% yield),with a very voluminous morphology and structure. Particulate structuresare not found in this comparative example, in analogy to ComparativeExample 2.

EXAMPLE 4 TO 8 Attempts to Prepare Microparticles From Starch IsolatedFrom Various Plants

500 mg of starch (see Table 1 for specification) are dissolved in 2.5 mlof dimethyl sulfoxide (DMSO, analytical grade, from Riedel-de-Haen) atabout 70° C. No solutions are formed. The mixtures form viscous gels.These are added with stirring to 100 ml of double-distilled water. Thegel disintegrates during this. The solution is kept at 5° C. overnight.Very cloudy suspensions with a large number of large white flakes form.Further processing is carried out as described in Example 1. The resultsof the examples are listed in Table 1. It is evident with all theComparative Examples 2 to 8 that the nonlinear polysaccharides or otherstarting materials differ very greatly from the results of the inventiondescribed in Example 1. Without exception there is formation of heavyturbidity and/or large flakes.

Structures with a particulate shape cannot be observed. In addition, theyields of solids in Comparative Examples 2 to 8 are distinctly less thanin Example 1.

TABLE 1 Results of the precipitation of various starch/DMSO solutions inwater Proportion of Consistency of linear the suspen- poly- Consistencyof sion after Final Ex- Starch saccharide the DMSO precipi- weight Yieldample type (%) solution tation at 5° C. (mg) (%) 1 1,4-α-D- 100 clear,low- fine, milky 311.0 62 Polyglucan viscosity suspension *¹ solution 2Amylose*² 90-100 dissolved after fine suspension 210.3 42 (EGA- 2 d,highly with flakes Chemie) viscous 3 Amylose*² 95-100 dissolved afterfine suspension 60.0 12 (Merck) 2 d, highly with flakes viscous onheating 4 Potato 20 solid gel, clear heavy turbidity not — Toffena ™separable (Südstärke) (centrifuge) 5 Corn starch 20 viscous gel slightturbidity, 83.8 17 (Merck) large flakes 6 Corn starch 50 viscous gelheavy turbidity, 101.7 20 C small flakes (National Starch) 7 Corn starch70 viscous gel heavy turbidity, 211.1 42 HVII small flakes (NationalStarch) 8 Peas 70 viscous gel, heavy turbidity, 115.9 23 (Amylose cloudylarge flakes KG) *¹water-insoluble *²water-soluble

EXAMPLE 9a AND b Preparation of Microparticles From 1,4-α-D-polyglucanon a Large Scale

a) 400 g of 1,4-α-D-polyglucan are dissolved in 2 l of dimethylsulfoxide (DMSO, analytical grade, from Riedel-de-Haen) over the courseof 1.5 h at 60° C. The solution is then stirred at room temperature forone hour. The solution is added through a dropping funnel to 20 l ofdouble-distilled water while stirring over a period of 2 h. The mixtureis stored at 4° C. for 44 h. A fine suspension forms. The particles areremoved by initially decanting off the supematant. The sediment issuspended and centrifuged in small portions (RC5C ultracentrifuge: 5000revolutions per minute for 5 minutes each). The solid residue issuspended in double-distilled water and centrifuged again a total ofthree times. The solids are collected and the suspension of about 1000ml is freeze-dried (Christ Delta 1-24 KD). 283 g of white solid areisolated (71% yield).

b) The collected supematants are kept at a temperature of −18° C.overnight. Processing takes place as described. A further 55 g of thewhite solid are isolated (yield 15%).

The overall yield of this process is thus 85% of colorlessmicroparticles.

EXAMPLE 10 Desulfurization of the Microparticles

The procedure for removing the dimethyl sulfoxide remaining in theparticles is as follows. 100 g of the 1,4-α-D-polyglucan from Example 9are added to 1000 ml of deionized water. The mixture is left for 24 hwith gentle agitation. Removal of the particles takes place as describedin Example 9 (RC5C ultracentrifuge: 3000 rpm for 15 minutes each). Thefinal weight after freeze drying is 98.3 g (98% yield). Determination ofsulfur by elemental analysis gives the following values (test methodcombustion and IR detection):

Sulfur content of the particles from Example 9: 6%+/−0.1%

Sulfur content of the particles from Example 10:<0.01%

EXAMPLE 11 Examination of the Solids From Examples 1 to 9 by ElectronMicroscopy

To characterize the particles, scanning electron micrographs (SEM)(Camscan S-4) are taken. The results of the examination are recorded inTable 2. It is clear from this that spherical microparticles areobtained only on use of water-insoluble linear polysaccharides(1,4-α-D-polyglucan). By contrast, the use of other initial polymersresults only in voluminous, cottony and nonparticulate morphologies forwhich a dispersity cannot be determined. The structure of the particlesobtained as in Example 1 is evident from FIGS. 1 and 2.

TABLE 2 Characterization of the solids and particles from Examples 1 to3 and 7 to 9 Proportion of linear poly- saccharide Example Starch type(%) Appearance of the particles 1 1,4-α-D- 100 round separate particlesPolyglucan*¹ 2 Amylose*² (EGA 90-100 flocculant, voluminous, Chemie)cottony (i.e. no separate particles) 3 Amylose*2 (Merck) 95-100flocculant, voluminous, cottony (i.e. no separate particles) 7 CornHylon VII  70 flocculant, cottony (National Starch (i.e. no separateparticles) Chemistry) 8 Peas (Amylose KG)  70 flocculant, cottony (i.e.no separate particles)  9a 1,4-α-D-Polyglucan 100 round separateparticles  9b 1,4-α-D-Polyglucan 100 round separate particles*¹water-insoluble *²water-soluble

EXAMPLE 12 Investigations of the Size Distributions of the ParticlesFrom Examples 1 and 9

Investigations are carried out with a Mastersizer (from MalvernInstruments) to characterize the size distributions of the particlesfrom Examples 1 and 9. The investigation took place in the Fraunhofermode (evaluation: multimodal, number) with a density of 1.080 g/cm³ anda volume concentration in the range from 0.012% to 0.014%. The resultsof this investigation are listed in Table 3 and show the greatuniformity of the microparticles.

EXAMPLE 13 In-vitro Production on 1,4-α-D-polyglucan in a BiocatalyticProcess Using Amylosucrase

10 l of a 20% strength sucrose solution are placed in a sterilized(steam sterilization) 15 l vessel. The enzyme extract containingamylosucrase is added in one portion. The enzyme activity in thisexperiment amounts to 16 units. The apparatus is equipped with alikewise sterilized all-glass stirrer. The vessel is closed and kept at37° C. with stirring. A white precipitate forms after a period of only afew hours. The reaction is stopped after a period of 180 hours. Theprecipitate is filtered off and washed five times with water to removelow molecular weight sugars. The residue remaining in the filter isdried in a drying oven at 40° C. under the vacuum of a diaphragm pump(CVC 2, Vacuubrand GmbH & Co). The mass amounts to 685 g (69% yield).The 1,4-α-D-polyglucan obtained in this way can be employed directly forcharacterization and for preparing microparticles.

EXAMPLE 14 Characterization of the Water-insoluble 1,4-α-D-polyglucanSynthesized With Amylosucrase From Example 13

2 mg of the 1,4-α-D-polyglucan from Example 13 are dissolved in dimethylsulfoxide (DMSO, analytical grade, from Riedel-de-Haen) at roomtemperature and are filtered (2 μm filter). One portion of the solutionis injected into a gel permeation chromatography column. DMSO is used aseluent. The signal intensity is measured by an RI detector and evaluatedby comparison with a pullulan standard (supplied by Polymer StandardSystems). The flow rate is 1.0 ml per minute.

The measurement shows a number average molecular weight (M_(n)) of14,200 g/mol and a weight average molecular weight (M_(w)) of 29,500g/mol. This corresponds to a dispersity of 2.1.

TABLE 3 Characterization of the particle diameters from Examples 1 and 9Particle distribution Example Diameter d d d Example d_(w)*² (10%)*⁴(50%)*⁵ (90%)*⁶ No. d_(n)*¹ (μm) (μm) d_(w)/d_(n)*³ (μm) (μm) (μm) 11.282 2.692 2.100 0.991 1.263 1.776 9a 1.664 4.184 2.541 0.873 1.5042.624 9b 0.945 2.345 2.481 0.587 0.871 1.399 *¹d_(n): number averagediameter *²d_(w): weight average diameter *³d_(w)/d_(n): dispersity ofthe particle diameters *⁴d(10%): 10% of all particles have a diametersmaller than the stated value *⁵d(50%): 50% of all particles have adiameter smaller than the stated value *⁶d(90%): 90% of all particleshave a diameter smaller than the stated value

What is claimed is:
 1. A process for preparing spherical microparticleswhich consists essentially of wholly or partly of a water-insolublelinear 1,4-α-D-polyglucan of class 6 or 7 as defined in DeutschesArzneibuch, which consists essentially of dissolving the water-insolublelinear 1,4-α-D-polyglucan in a solvent, introducing the solution into aprecipitant, cooling the mixture resulting therefrom, and removing themicroparticles formed and said solvent is dimethyl sulfoxide, formamide,acetamnide, N,N-dimithylformamide, N,N-dimethylacetamide,N-methylmorpholine N-oxide or dichloromethane.
 2. The process as claimedin claim 1, wherein said solution and said precipitant are mixed attemperatures from 20 to 50° C., and the mixture is cooled totemperatures from +10 to −100° C.
 3. The process as claimed in claim 1,wherein said solvent is dimethyl sulfoxide.
 4. The process as claimed inclaim 1, wherein said precipitant is water or an aqueous medium.
 5. Theprocess as claimed in claim 1, wherein the solution is prepared in thepresence of one or more biodegradable polymers and/or of one or moreactive substances.
 6. The process as claimed in claim 1, wherein themixture is cooled to temperatures from 5 to −5° C.